The present invention relates to a method and a system for recovery of refrigerants or other volatile liquids from closed working circuits, e.g. from refrigeration units to be scrapped or repaired, or for purifying the refrigerant of a given system and then returning it to the same system for re-use. Care should be taken to prevent the gases from escaping to the atmosphere, where they are highly undesired. Normally, used refrigerants are polluted, e.g. by water and oil, and for enabling them to be reused it is required to subject them to an effective purification.
These problems have already been described and discussed in detail in many patent specifications, of which a few examples are the U.S. Pat. Nos. 4,285,206, 4,441,330, and 4,476,688. Of still higher relevance is the U.S. Pat. No. 5,094,087, belonging to the present assignee. According to the latter specification it is proposed that the recovery system comprises a suction inlet separator container, also called a suction accumulator, connected with the suction side of a compressor and with an intake conduit for connection with the external system, the regrigerant of which is to be recovered and reclaimed. Thus, as usual, the refrigerant is recovered in its gaseous phase and supplied to the compressor, from the discharge side of which it is supplied to a cleaning system including filter means for extracting moisture and other impurities from the gaseous refrigerant, whereafter the purified gas is delivered to a condenser that enables the refrigerant to be supplied to a collector tank for purified, liquid refrigerant.
It has been found, in that connection, that it is easier and better to purify the refrigerant in its gaseous state rather than in its liquid state, and this is still held to be true, generally.
There are four main contaminants in the refrigerants, viz. oil, acid, water and air, besides particular impurities, and in the prior art it has been a natural tendency to seek to improve the relevant separation means for each of these contaminants, for example resulting in quite effective and specialized oil and water filtration units. Over the recent years, however, the requirements as to the degree of purification of the reclaimed refrigerants have been ever rising, and it has been found that the highly developed filter units for the respective contaminants are not always as effective as desired or as believed.
In connection with the present invention, it has been found that when it comes to really high requirements as to the purification it is no longer possible to rely on the use of respective unitary filtration units for the different contaminants, at least as far as the oil, the acid, and the water are concerned. In fact, the picture becomes very complex when it is desired to improve further the purification at the higher end of the scale, for example speaking of purities higher than 99%. Prior purification systems may well have operated satisfactorily for removing as much as 95% of the contaminants, based on the effect of the respective specialized separator means, but in the very last end of the scale this is not at all sufficient.
Thus, it has been found that while good oil and acid filter units may remove, say, 95% of the contaminants attempts of improving further the units generally fail, because the filter units tend to become selective. Sometimes they operate with high efficiency, yet other times they are not so effective. Apparently, they--or rather the whole system--become sensitive to the detailed composition of the recovered contaminated refrigerant as well as to the ambient temperature.